Who is Renzo Leoni from A Thread of Grace and what is their importance?

Also known as Ugo Messner, Stefano Savoca and Don Righetti, Renzo is the main character in the story whose experience as a pilot in the Absynnian war took a toll on his conscience and affected his entire life. Renzo felt that if he continued to feel guilty it would justify the fact that he lived on after bombing a hospital full of patients in Africa. He is a heavy drinker and a master of disguises and languages, and is one of the most endearing characters in the novel.